Phenylethanolamines illustrated by the structure: ##STR1## wherein R.sub.1 is H, halo or CN; R.sub.2 is F, CF.sub.3, NO.sub.2 or CN and R.sub.3 represents a variety of substituents, such as (C.sub.3 -C.sub.5) alkyl and (C.sub.3 -C.sub.5) cycloalkyl; are reported in U.S. Pat. No. 4,119,710 as analgesics, uterospasmolytics, bronchospasmolytics and antispastics for the skeletal musculature, and especially as .beta..sub.2 -receptor mimetics and .beta..sub.1 -receptor blockers. Other related dihaloamino- and monohaloamino-phenylethanolamine compounds with similar biological activity are disclosed in U.S. Pat. Nos. 3,536,712 and 3,574,211.
In U.S. Pat. No. 4,407,819, many of the above said compounds as well as a variety of other phenylethanolamine derivatives are described as agents useful for increasing lean meat deposition and/or improving the lean meat to fat ratio of warm-blooded animals, such as swine, poultry, sheep, goats, cattle and domestic pets.
Still other phenylethanolamine derivatives are disclosed in U.S. Pat. No. 4,404,222 and are said to be agents useful for increasing the growth rate of meat producing animals and improving the efficiency of feed utilization thereby.
Recently, Offenlegungsschrift DE No. 3,306,159 A1 (European Patent Application No. 103830) was published describing substituted phenylethylamine derivatives which were said to be growth promoters for pigs, cows, poultry, cats, dogs, rabbits, fur animals, fish, and reptiles.
In a pending U.S. patent application Ser. No. 714,240, 3-[(2-tert-butylamino)-1-hydroxyethyl]-5-fluorobenzonitrile and 3-fluoro-5-[1-hydroxy-2-(isopropylamino)ethyl]benzonitrile were also described as new compounds for increasing the lean meat to fat ratio and/or improving the efficiency of feed utilization, and/or enhancing the growth rate of warm-blooded animals.
While the above-said phenylethanolamine derivatives demonstrate utility for the purposes described, it would be advantageous if still other new compounds could be found that are more potent for increasing the lean meat to fat ratio of meat producing animals, improving the growth rate thereof and/or enhancing the efficiency of feed utilization thereby. It would also be especially advantageous if the novel phenylethanolamines would exhibit less .beta..sub.1 heart stimulant activity and would shown an improved margin of safety over the known phenylethanolamines and would not be subject to residue retention in the animal tissues.